The theme of corruption is introduced by Sweeney in the opening scene, where he portrays London as "a great black pit" teeming with "the vermin of the world." In Sweeney's depiction, morality is nonexistent in London, as "at the top of the hole / Sit the privileged few / Turning beauty into filth and greed." Judge Turpin is a prime example of these elite individuals, dispensing "justice" driven by his own selfish motives. He falsely accuses Sweeney and sends him to an Australian penal colony, clearing the path for Turpin to pursue Sweeney's wife. Turpin's hypocrisy is clear in his interactions with a young boy in his courtroom. Although he professes his "earnest wish ever to temper justice with mercy," he decides against leniency for a repeat offender, sentencing the boy to death while scheming to force Johanna, his ward, into marriage to fulfill his desires.

The play also illustrates how the lower classes are pushed toward similar corruption in a system that strips them of dignity. The extreme poverty in Victorian London, with no social safety nets, drives people to resort to blackmail and murder for survival. Mr. Pirelli blackmails Sweeney when he threatens his business by outperforming him in a barbering contest. Sweeney and Mrs. Lovett resort to murder, driven by revenge and greed, seeing no other option for their dismal lives. Sweeney becomes obsessed with avenging the wrongs done to his family, while Mrs. Lovett assists him to sell enough pies to keep a roof over her head.

The widespread corruption in the city strips the characters of their innocence. Sweeney reflects on his naive hope that he and his wife, who was "his reason and his life," could find happiness together. This hope is dashed when Judge Turpin, described as "a pious vulture of the law," tears their family apart. Sweeney becomes a disillusioned cynic, warning Anthony, whose youthful innocence makes him declare London as the best place in the world, "You are young. Life has been kind to you. You will learn."

Lucy's loss of innocence is even more devastating after Sweeney is imprisoned. Assaulted by Judge Turpin and abandoned by a society that offers no support to a disgraced woman, Lucy, once beautiful and virtuous, is left tainted. To survive, she resorts to begging and selling her body on the streets of London.

A key theme of the play is Anthony and Sweeney's resolve to protect Johanna from Judge Turpin's attempts to rob her of her innocence, as he did her mother. Although Anthony ultimately saves Johanna's virtue, she first endures the harsh realities faced by London's poor in mental institutions. This ordeal, along with Judge Turpin's abuse, hardens Johanna to the point where she is willing to shoot the asylum owner to break free.

The widespread corruption and loss of innocence that Sweeney experiences ignite his obsession with revenge. His primary target is Judge Turpin and the Beadle, seeking retribution for the injustices they inflicted on his family. Yet, when Pirelli threatens to disrupt his plans, Sweeney begins a killing spree, extending his vengeance to encompass both social and personal justice. Alongside Mrs. Lovett, who is solely driven by greed, Sweeney concludes that "the history of the world . . . is who gets eaten and who gets to eat." Consequently, he decides to "practice on less honorable throats," aiming to shift social power to the lower classes until he can finally exact revenge on Judge Turpin. Sweeney's relentless pursuit, however, spirals into madness, ultimately leading to his downfall.